1. Field of the Invention
The present invention generally relates to implantable prosthetic devices, and more particularly, the present invention relates to an implantable prosthetic heart valve and a method for manufacturing thereof.
2. Description of Related Art
Replacement valves in a patient and in machines for mimicking valves in a patient are known in the medical field. For example, valvular heart disease (VHD) remains a significant public health issue affecting 1-2% of Americans with an estimated 2-4% of people over the age of 65 suffering from aortic valve stenosis. Currently, when extensive heart valve damage has occurred in a patient's heart, for example from heart disease or a birth defect, one remedy is to replace the heart valve surgically. Current treatment includes open-heart surgical replacement of the diseased valve with either mechanical or tissue prosthetic heart valves (PHV). The replacement heart valve may be an artificial device or an animal tissue valve (e.g., bovine pericardium or porcine aortic valve). For example, one type of heart valve which has been the subject of replacement valves are aortic valves. Presently, artificial (mechanical) heart valves are not as prevalently used as animal tissue valves. One reason is artificial valves such as polymer PHVs are unsatisfactorily susceptible to damage caused by stresses from flexing and operation during use, i.e., material fatigue. Since 1960, various devices and techniques have been used for replacement valves and delivery or implantation of the valve.
Referring to FIGS. 1-3, a prior art trileaflet heart valve 10 includes three leaflets 14, 16, 18, and a stent structure 20 having three posts 22. The stent structure 20 supports a multilayer composite polymeric membrane that is a flat sheet membrane sewn into the shape of three leaflets 14, 16, 18, each having a uniform thickness. The one-piece multilayer composite polymeric membrane of the leaflets 14, 16, 18 is composed of a porous polymeric structure (e.g. a knit, weave, braid) sandwiched between two outer polymer layers. An example of such a one-piece multilayer composite polymeric membrane and heart valve as described is US Patent Application publication 2007/0118210 (pub. date May 24, 2007), Ser. No. 11/561,069, filed on Nov. 17, 2006.
One disadvantage of the above prior art heart valve is undesirable stress wear on the leaflets results in fatigue of the leaflets. The polymer in the prior art was a thermoplastic elastomer with low tensile strength and was prone to significant creep. The embedded mesh was designed to add strength. However, in animal testing the polymer creep exposed the underlying mesh to blood and caused an adverse reaction. Further, the above heart valve requires a multilayer composite approach that is undesirably complex to manufacture and expensive. It also does not allow for fine tuning of the leaflet thickness to improve flexibility and durability. A disadvantage of using animal tissue in replacement heart valves is that chemically fixed animal tissue valves require animal tissue sourcing, handling, processing, sterilization and packaging. Further, other disadvantages from current heart valve implantation are present from the risk to a patient receiving animal tissue heart valves, that is the implanting of xenografts, because of the differences in tissue degeneration, or tissue lifespan, between species of animals and humans, and also the possibility of transfer of diseases from the animal to a human. Also, the durability of animal tissue valves is highly dependent upon the application and the health and age of the patient. There has therefore been a long felt need in the industry for a valve, and particularly a heart valve to remedy the disadvantages described above. Additionally, mechanical valves require lifelong anticoagulant drug therapy which includes significant risk of bleeding and stroke. Polymeric trileaflet valves may eliminate the disadvantages of current heart valve prosthetics.